Since this games really plays with the type of damage you do (blunt, slash, thrust etc.)

Do you guys recommend i upgrade 2 different type of weapon ?

It's not like anything can't be tackled with one but it all really depends on the moveset of the weapon. I would say that blunt weapons sure do make short work of skeletons in 4-1 and so forth but other than that you'll be fine with a single wepaon for the whole game as long as you feel comfortable using it.

Depends on the weapons you pick up. I use pokey shit for the guys in Stonefang but only if I haven't got a good main option.

Not the answer you're looking for, but it depends on the weapons and your build. Most people will tend to take a different route through the game depending on what their build is and what items they're prioritizing first for that playthrough, so often the damage type resistances can be overpowered by sheer power at a certain point.

Obviously you can also do stuff like 'get A to get B to get C' etc., which is what I typically do on a playthrough where I don't have something preplanned. Something like Mail Breaker from 1-1 to kill miners in 2-1/2-2 to get Dragon Longsword from 2-2 to kill guys in 5-1 to get Blessed Mace from 5-1 to kill skeletons in 4-1 to farm the reapers/rescue Saint Urbain in 4-2 to kickstart a playthrough, for example. The more times you play through a Souls game, the more routes you'll find like the above that open up to you to make starting a new character easier. In Dark Souls 1, you can basically have a completed character build before you even fight the first non-tutorial boss if you take the Master Key, depending on what you're going for.

All I know is that, according to Breaking Brad, you should use your fists on those skeletons in world 4.